Interference suppressor

ABSTRACT

A suppression device for an electronic appliance having a plug-in device which has at least one plug-in element and is designed for attachment to a housing of the electronic appliance, with a capacitor having at least two capacitor plates being provided in order to improve the electromagnetic sensitivity. In a simple and low-cost suppression measure for electronic appliances, which is also suitable for mass production, the capacitor is arranged outside the housing of the electronic appliance and is electrically connected firstly to a plug-in element of the plug-in device and secondly to the potential of the electrically conductive housing.

DESCRIPTION

The invention relates to a suppression device for an electronicappliance having a plug-in device which has at least one plug-in elementand is designed for attachment to a housing of the electronic appliance,with a capacitor being provided in order to improve the electromagneticsensitivity.

In order to ensure correct operation of electronic devices, thesedevices must be shielded against interference radiation which occurs inparticular in the radio-frequency band. Such suppression measures arenormally carried out on a printed circuit board which is located in theinterior of the electronic appliance.

DE 33 26 629 C2 discloses an interference protection filter forelectronic controllers in a motor vehicle, in which the interferenceprotection filter is arranged directly adjacent to the input of the plugconnections in the housing. A capacitively acting switching element inthis case has two capacitor plates, with one capacitor plate being inthe form of a line which leads to the electronic circuit from that endof a connector which projects into the electronic appliance.

This has the disadvantage that this suppression device can onlyattenuate interference radiation, since the supply line which isconnected to the suppression device still radiates power, and this has anegative effect on the electronic components.

Standard bushing capacitors which are normally used for suppression andare soldered into metal housings are expensive and complex to process.

SUMMARY OF THE INVENTION

The invention is thus based on the object of specifying a simple andlow-cost suppression measure for electronic appliances which are alsosuitable for mass production.

According to the invention, the object is achieved in that the capacitoris arranged outside the housing of the electronic appliance and iselectrically connected firstly to a plug-in element of the plug-indevice and secondly to the potential of the electrically conductivehousing.

The invention has the advantage that the suppression is actuallyprovided on the outside of the electronic appliance, and interferenceradiation cannot enter the housing interior at all. Such a suppressiondevice is simple to install since the insertion of the connector intothe housing produces a suppression filter. There are no additionalinstallation measures.

In order to make it possible to dispense with cables to the capacitor, afirst capacitor plate is formed in or on the plug-in device.

The first capacitor plate is advantageously formed from the plug-inelement itself. This can easily be achieved, for example, by upsettingthe connector pin. This further simplifies the production of theconnector.

Alternatively, the first capacitor plate is formed by a conductorsurface which is arranged on a mounting element, is arranged alongsidethe plug-in element and is electrically connected to it. This is donesimply by the first capacitor surface enclosing the plug-in element,which has no insulation and carries an electrical potential, in aninterlocking and/or force-fitting manner. This results in a device whichcan be handled particularly well for mass production.

The mounting element advantageously has at least one further conductorsurface, which forms the second capacitor plate and is arranged aboveand/or underneath the first conductor surface, electrically isolatedfrom it. The mounting element together with the two capacitor plates canbe prefabricated, so that only the electrical connection still needs tobe produced during connector installation.

In a development of the invention, a conductor surface which forms thesecond capacitor plate is in the form of a contact coating on onesurface of the mounting element. In this case, there are two possibleways to produce the electrical connection for the housing potential.

Firstly, the electrically conductive contact coating of the mountingelement is located directly on the outside of the housing, resulting ina conductive connection and in the contact coating assuming the housingpotential. In this arrangement, there is no need whatsoever for anyadditional conductive connections.

The contact coating is advantageously in the form of a conductiveadhesive, so that the mounting element is at the same time attached tothe housing.

In another refinement, the electrical connection between that conductorsurface of the mounting element which forms the second capacitor plateand the housing is produced by means of at least one attachment elementwhich holds the mounting element and/or the plug-in device on thehousing.

The housing potential is in this case produced via a screw, riveted orpress-in connections, which are present in any case, at at least onepoint.

If the second conductor surface is in the form of a contact surface,insulation is arranged between it and the outside of the housing. Inthis case as well, the plug-in device is located in an unchanged mannerand firmly on the housing outer wall.

In order to form a further capacitor for the same plug-in element, themounting element has two further conductor surfaces, which are locatedone above the other and are electrically isolated from one another, withthe third conductor surface being electrically connected to the plug-inelement and the fourth conductor surface being electrically connected tothe housing potential. This multilayer construction allows largercapacitance values to be achieved for each connector pin.

In one simple refinement, the plug-in device has a number of plug-inelements, with the first capacitor surfaces, which are electricallyisolated from one another and are associated with different plug-inelements, being formed in a conductor coating.

The second capacitor surface is formed by the unstructured contactcoating for all the plug-in elements. An arrangement such as this caneasily be produced by means of film printed circuits.

In one advantageous development, the mounting element can be fitted onthat side of the plug-in device which faces the housing and can be madecontact with in that a first capacitor surface in each case encloses ineach case one plug-in element.

A commercially available connector can thus be provided with anadditional suppression device according to the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention allows numerous embodiments. One of these will beexplained in more detail with reference to the figures which areillustrated in the drawing, in which:

FIG. 1: shows a section through a controller

FIG. 2: shows a first embodiment of the suppression board

FIG. 3: shows a second embodiment of the suppression board

FIG. 4: shows a third embodiment of the suppression board.

Identical features are identified by the same reference symbols.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 1 shows an electrical appliance as is normally used in motorvehicles. This may be a controller for a motor vehicle, which hassignal-processing electronics which, as is known, are highly susceptibleto interference at radio frequencies. However, it is also feasible forthe electronic appliance to be a sensor device which, in addition to anactual sensor, has a signal processing circuit and/or a signalevaluation circuit, which are/is arranged on one or more printed circuitboards.

The electronic appliance has a cup-shaped housing part 1 which iscomposed of aluminum and is sealed by a cover 2.

The cup-shaped housing part 1 has a connector body 3, which is attachedon the outside to the housing part 1 by means of screws or rivets 4. Theconnector pins 5 of the connector body 3 project not only into theconnector body 3 but also into the housing interior 6. The connector 3connects the appliance circuits via the connector pins 5 to otherelectronic devices in the motor vehicle.

At least one printed circuit board 7 is arranged in the housing interior6 and is populated with components 8 which provide electronic circuits.The connector pins 5 which project into the housing interior 6 areelectrically connected to the components 8 that are located on theprinted circuit board 7, in order to supply signals and electricalpower.

A suppression board 9 is inserted between the connector 3 on the outsideof the housing part 1, and is attached to the housing part 1 togetherwith the connector 3.

FIGS. 2-4 explain various embodiments of the suppression board 9 in moredetail.

FIG. 2 shows a suppression board 9 with openings 13 for the connectorpins 5. In addition to these openings 13, a discrete capacitor 10 isprovided for each connector pin 5 and is connected by means of wiringthat is arranged on the board 9, such that each capacitor 10 isconnected firstly to the connector pin potential and secondly to thepotential of the housing 1. In this case, the housing potential isnormally ground.

The prefabricated board 9 is pushed over the connector pins 5, with acircumferential connector seal 12 enclosing the suppression board 9 atits edge, and sealing it at the same time. The suppression board 9 isattached to the outer skin of the housing part 1 by means of screws 4which engage in the openings 11 in the suppression board 9 and in theopenings 14 in the connector body 3. It is attached such that the seal12 rests on the housing part 1. The screws 4 at the same timeelectrically connect the capacitors 10 to the housing potential.

Another embodiment, in which capacitances are integrated in thesuppression board 9, is shown in FIG. 3. The suppression board 9 is inthe form of a board without any components, for example a film printedcircuit, and has a structured conductor coating 15. The structurecorresponds to individual capacitor surfaces 16 which are isolated fromone another. In this case, a capacitor surface 16 is provided for eachconnector pin 5 and encloses the opening 13 of the respective connectorpin 5. These openings 13 are metalized, with each capacitor surface 16being connected to the metalized opening 13 at the boundary surface,thus producing an electrical connection. After insertion of theconnector pins 5, the capacitor surfaces 16 are at the connectorpotential. In this embodiment, push-processes are particularlyadvantageous as electrical connection mechanisms for making contact,where the plug-in elements 5 are made contact with by pushing them intothe suppression board 9. If the plug-in element 5 has two push-in zones,which are not shown in any more detail, the pushing-in process makescontact both with the suppression board 9 and with the printed circuitboard 7.

The filter plate 9 has a further conductive coating 18 on the surfacefacing the housing, and this further conductive coating 18 restsdirectly on the housing 1 once the connector 3 has been fitted. It thusassumes the housing potential, with the conductive housing 1 forming thesecond capacitor plate. The unstructured conductive surface 18 ispreferably in the form of conductive adhesive, in order to attach thesuppression board 9 to the housing.

This refinement results in each connector pin 5 itself acting as acapacitor plate and, together with the housing part 1 that is connectedto ground, forming a suppression capacitor.

FIG. 4 shows a further embodiment. The suppression board 9 is in theform of multilayer [lacuna] formed from conductor surface coatings whichare pressed to one another and have fabric-reinforced synthetic resincoatings located in between (FR4 base material). According to thisembodiment, the filter board 9 is provided with four copper layers 19,20, 21, 22. One copper layer 19 and 22 is arranged on each of the twoouter faces of the board 9. Two further copper layers 20, 21 are locatedwithin the suppression board 9, isolated from one another, and form thecapacitor surfaces 16, as has been described in conjunction with FIG. 3.

The two outer copper layers 19, 22 are connected to the housingpotential via the attachment elements 4 and are electrically isolatedfrom the potential carried by the connector pin 5. These copper layers19, 22 are connected via a number of through-plated contacts, which arenot shown in any more detail but are arranged such that they enclose thecapacitor surfaces 16, thus providing shielding. The capacitor surfaces16 are electrically connected to the connector pins 5 in the manneralready described. Two capacitors are thus provided for each connectorpin. If even more capacitors are required, then this can easily beproduced by means of further alternate installation of copper layers 20,21, which form the structured capacitor surfaces 16, and unstructuredcopper layers 19, 22, which are formed over the entire surface and areat the housing potential.

If necessary, a large number of such mutually isolated conductorsurfaces 19, 20, 21, 22 can be arranged within the suppression board.

In addition to the explained embodiment, the capacitor surfaces 16 mayalso be formed using stamped parts or Kapton films, which are embeddedin an insulating material. At the same time, this may carry out sealingtasks, depending on the material or material combination used to sheaththe capacitor plates.

These capacitor surfaces according to the invention form capacitances inthe range up to 100 pF with the outer housing. In addition to a directelectrical connection between the capacitor and the plug-in element 5 orthe electrically conductive housing 1, it is, however, also sufficientto improve the electromagnetic sensitivity, for there to be onecapacitive coupling. The critical feature is that the suppression board9 which forms the capacitor is itself not surrounded by an electricallyconductive housing. The suppression board 9 is in this caseadvantageously integrated in a plastic appliance connector, or issurrounded by such a connector.

We claim:
 1. A suppression device for an electronic appliance having aplug-in device which has at least one plug-in element and is designedfor attachment to a housing of the electronic appliance, the suppressiondevice comprising a capacitor provided to improve electromagneticsensitivity, wherein the housing is an electrically conductive housing(1, 2), and wherein the capacitor (10) is arranged outside the housing(1, 2) of the electronic appliance and is electrically connected firstlyto the plug-in element (5) of the plug-in device (3) and secondly topotential of the electrically conductive housing (1, 2).
 2. Thesuppression device am claimed in claim 1, wherein a first capacitorplate (16) of the capacitor (10) is arranged in or on the plug-in device(3).
 3. The suppression device as claimed in claim 2, wherein the firstcapacitor plate (16) is formed from the plug-in element (5) itself. 4.The suppression device as claimed in claim 2, wherein the firstcapacitor plate (16) is formed by a first conductor surface (15)arranged on a mounting element (9), is arranged alongside the plug-inelement (5) and is electrically connected thereto.
 5. The suppressiondevice as claimed in claim 4, wherein the first conductor surface (15)is a first capacitor surface, and the mounting element (9) has at leastone second conductor surface (18), which forms a second capacitorsurface and is arranged above and/or underneath the first conductorsurface (15), electrically isolated therefrom.
 6. The suppression deviceas claimed in claim 5, wherein the electrical connection between thesecond conductor surface (18) of the mounting element (9) and thehousing (1, 2) is produced by at least one attachment element (4) whichholds the mounting element (9) and/or the plug-in device (3) on thehousing (1, 2).
 7. The suppression device as claimed in claim 5, whereinthe second conductor surface (18) forms a second capacitor plate and isin form of a contact coating on a surface of the mounting element (9).8. The suppression device as claimed in claim 7, wherein insulation (17)is arranged between the contact coating (18) and an outside of thehousing (1, 2).
 9. The suppression device as claimed in claim 7, whereinthe contact coating (18) of the mounting element (9) is located directlyon the outside of the housing (1, 2).
 10. The suppression device asclaimed in claim 9, wherein the contact coating (18) is in the form ofconductive adhesive.
 11. The suppression device as claimed in claim 5,wherein the mounting element (9) has two further conductor surfaces (19,20; 21, 22) comprising a third and fourth conductor surface, which arelocated one above the other and are electrically isolated from oneanother, in order to form a further capacitor for same said plug-inelement (5), with the third conductor surface (20, 21) beingelectrically connected to the plug-in element (5) and the fourthconductor surface (19, 22) being electrically connected to the housingpotential.
 12. The suppression device as claimed in claim 11, whereinthe plug-in device (3) has a number of plug-in elements (5), with thefirst capacitor surfaces (16), which are electrically isolated from oneanother and are associated with different of said plug-in elements (5),being formed in a conductor coating (15).
 13. The suppression device asclaimed in claim 11, wherein the second capacitor surface is formed byan unstructured contact coating (18) for all the plug-in elements (5).14. The suppression device as claimed in claim 12, wherein the mountingclement (9) is fitable on a side of the plug-in device (3) which facesthe housing (1, 2) and is made contactable with in that the firstcapacitor surface (16) in each case encloses in each case one saidplug-in element (5).